1. Field of the Invention
This invention relates generally to an airfoil of cambered character which is adjustably self-cambering in response to variations in wind speed and direction. The invention also relates to a craft, e.g., a boat, comprising such airfoil.
2. Description of the Related Art
In the deployment and use of sail craft, e.g., sailboats, iceboats, etc., which utilize wind as a motive power source, the aerodynamic principles of thrust (lift) and drag govern the efficiency of the sail or airfoil member.
In an effort to improve the aerodynamic efficiency of sail craft, wing-type airfoils have been evolved which typically include a framework supporting a double-surfaced shroud constructed of flexible material which is deformable in response to impingement of wind thereon. These double-surfaced wing-type airfoils have been constructed to provide a cambered airfoil shape on one of the main shroud surfaces, i.e., a convex curvature from a leading edge region of the shroud surface to the trailing edge region of such surface, to mimic the shape and achieve the high lift, low drag performance of a fixed (aircraft-type) wing.
U.S. Pat. No. 4,437,426 issued Mar. 20, 1984 to Ronald D. Latham discloses a wing type airfoil assembly suitable for use on boats or other craft, which comprises a central load carrying spar having disposed about its opposite ends an upper tip member and a lower root member. A flexible cable is interconnected in a general loop fashion around and between the tip and root members, with a forward run spaced forwardly of the spar and a rear run spaced rearwardly of the spar. A slat is secured to the forward run of the cable, with the trailing edge of the slat being in spaced relationship to the spar to define a slot area therebetween. A skin covering extends between the rear run and the spar, and is wrapped around the spar to create a double surface wing panel whose leading edge is formed by the spar and whose trailing edge is formed by the rear run of the cable. The spar of this assembly is reposed in a journaled arrangement over a holding shaft secured in turn to the craft so that the entire assembly is rotatable about the holding shaft in response to wind speed and direction.
U.S. Pat. No. 4,530,301 issued Jul. 23, 1985 to Ronald D. Latham describes a variable camber airfoil assembly including a rigid leading edge member pivotally mounted about the leading edge of the airfoil such that it can move from side-to-side in order to improve the entry of the airfoil into the wind. The means for limiting side-to-side movement of the rigid leading edge member comprises a mast extending substantially the entire length or height of the wing-type airfoil and extending between two laterally spaced sides forming the rigid leading edge member.
U.S. Pat. No. 4,369,724 issued Jan. 25, 1983 to John Weiss describes a sail comprising two symmetric fabric sections attached together at the edges to form a fabric skin which is suspended by an edge tension mechanism functioning to control forward and trailing edge tension to tune and reverse the airfoil section. The sail's fabric sections are supported by an internal arrangement of a mast and a curved boom, with a control rope slideably connected to the mast at the internal mast boom connection. The control rope is tensioned and the mast is moveable in either direction along the boom to set up differential tensional relationships between the respective edges of the sail to in turn impart a desired airfoil shape to the sail in either direction.
U.S. Pat. No. 4,649,848 issued Mar. 17, 1989 to Mark S. Belvedere discloses a sail assembly having a sock enclosing the mast and a main section with a trailing edge. The main section joins the sock at a sock seam. A plurality of batten pockets are provided on the main section and extend freely within the sock to near the mast. Flexible rib pairs opposite the mast are clamped tangentially to full length battens, with the battens defining the shape of the ribs and the orientation of the leading edge. The assembly is adapted to automatically position the leading edge member into relative wind and to define a smooth aerodynamic shape of the sock blending with both sides of the main section as the sail is variously trimmed.
U.S. Pat. No. 4,685,410 issued Aug. 11, 1987 to Robert R. Fuller describes an airfoil sail system for a boat having a mast, comprising a front airfoil which is pivotal about an axis defined by the mast and which has leading and trailing edges. A rear airfoil is also provided which has leading and trailing edges. The front and rear airfoils are operatively coupled by a coupling means so that rotation of the front airfoil about its axis effects a counter-rotation of the rear airfoil to permit adjustment of the camber of the airfoil sail system.
U.S. Pat. No. 4,848,258 issued Jul. 18, 1989 to Paul D. Priebe describes an airfoil system for water vessels, comprising at least one mast to which a plurality of yards are attached. The yards are in the shape of an airfoil that is symmetrical from front to back, and asymmetrical from side to side. Fabric attached to the periphery of the yards forms the surface of the sail, with the mast enclosed in the sail. The mast is rotatable to sail at different angles to the wind and to allow tacking.
U.S. Pat. No. 4,972,789 issued Nov. 27, 1990 to Luigi Greppi discloses a sailboat mast structure comprising a tubular body with anchor means for two distinct sailcloths forming a wingsail. The tubular body has a cross section divided in two parts by an axis transverse to the longitudinal axis of the boat; a first part faces the bow, and a second part faces the stern. The first part has a markedly convex or substantially semielliptical curved profile. The second part has a rounded tip profile or a substantially semicircular profile. The anchor means are positioned along two generatrices crossing two points which are symmetrical in respect of the center or coinciding with the center of the first part.